1. Field of the Invention
The present invention relates to a lens barrel, in particular to a lens barrel in which movable members move in an optical axis direction by rotation of a cam ring incorporated in the lens barrel.
2. Description of the Related Art
A lens barrel in which the relative position between a lens group closest to the object side (hereinafter referred to as a front lens group) and a lens barrier in an optical axis direction changes is known in the art as a type of lens barrel which shields an opening thereof in front of an optical system (photographing optical system/imaging optical system) by the lens barrier (generally composed of one or more barrier blades) when moving from a ready-to-photograph state to a lens barrel accommodated state (lens barrel retracted state). When the lens barrel is in the lens barrel accommodated state, in which the lens barrier is shut, the front lens group is retracted relative to the lens barrier to be prevented from interfering with the lens barrier. When the lens barrel is in a ready-to-photograph state, the front lens group is extended out forward relative to the lens barrier in a manner to prevent vignetting of incident light which may be caused by the inner edge of the opening of the lens barrier.
In the case of controlling differentially driven members such as the front lens group and the lens barrier using cam grooves formed on a cam ring, two types of cam grooves having different cam contours are formed on a periphery of the cam ring, which tends to add constraints to miniaturization of the cam ring, mainly in the optical axis direction. Specifically, if two or more types of cam grooves which are formed on the same peripheral surface (inner or outer periphery) of a cam ring have a nonlinear cam track as disclosed in Japanese Unexamined Patent Publication No. 2004-258646, the cam grooves are easily interfere with each other; additionally, it has been difficult to position the two or more types of cam grooves, which are formed on the same periphery of the cam ring, close to one another as possible so as to have a minimum distance therebetween. To overcome this problem, in Japanese Unexamined Patent Publication No. 2009-222875, the two types of cam grooves formed on a peripheral surface of a cam ring are formed as linear lead grooves, and a nonlinear moving path is given to a movable member by a complementary cam mechanism provided separately from the aforementioned linear lead grooves. The formation of the plural types of grooves as lead grooves improves the space utilization on the periphery of the cam ring and makes it possible to achieve miniaturization of the cam ring.
In lens barrels of the related art, two types of cam grooves like those described above are each formed on a cam ring as a cam groove having a full cam track that covers the entire moving range of an associated movable member, the movement of which is controlled by the associated one of the two types of cam grooves. Therefore, an improvement in space utilization by formation of each cam groove as a lead groove can be achieved like in the case of the above-mentioned Japanese Unexamined Patent Publication No. 2009-222875; however, since two types of full-shape cam grooves (including lead grooves) need to be formed on the same peripheral surface (outer or inner periphery) of the cam ring, there still have been constraints in space utilization, limiting the miniaturization of the cam ring.